With the aid of computed tomography (CT), suitable measuring and evaluation methods can be used to provide information on the essential relevant diagnostic parameters of an examined organ, in particular a heart. In particular in the case of examinations in the region of the heart, it is important that as many clinically relevant parameters as possible are acquired with high precision and little stress on the patient, i.e. the lowest possible X-ray dose and quantity of contrast medium.
During heart examinations, computed tomography is currently mainly used to perform the following main evaluations, which generally require a plurality of very different measurements to be performed:
1. Detection and evaluation of calcification in coronary vessels, on cardiac valves and the aorta. Here, usually a simple measurement of the cardiac region is sufficient, i.e. a single scan covering the cardiac region without any contrast medium.
2. Analysis of the coronary vessels for the diagnosis of coronary heart disease. According the current state of the art, for this the heart is recorded by way of plurality of measurements at different time points of the heartbeat (i.e. in different cardiac phases). The dose required for this currently lies in the region of 5 to 10 mSv. The data are then usually analyzed slice by slice in that the inner and outer contours of the cardiac muscle of the left and/or right ventricle are determined automatically or interactively.3. Functional analyses of the heart, such as, for example, spatial and temporal analysis of the left and right ventricles to determine the shape and volume change of the myocardium and myocardial mass and ejection fraction. Nowadays, this is usually done by taking a so-called multiphase scan, wherein for a kinetic analysis of the heart, generally virtually the entire cardiac cycle is determined as a four-dimensional volume. This means a 4D image data record is generated containing three-dimensional spatial image data at different time points or movement phases, which ultimately corresponds to a sort of film of the motion of the heart.4. Perfusion measurements to investigate the blood supply to the cardiac muscle and for determining diagnostic parameters relating to the blood volume and blood flow. For this, different contrast medium images are produced, optionally also at different time points of the passage of the contrast medium. With many methods, time-resolved measurements of the heart volume are also performed, i.e. once again a type of 4D image data record is recorded.
More modern high-end computed tomography systems use helical scan methods with a particularly high pitch, which enable the acquisition of images of the heart in a so-called “flash mode”. Acquisition in “flash mode” is frequently performed using a dual-source-computed tomography system with a movable patient's bench moving at speeds of, for example 40 cm/s, during the recording. This enables a heart (measuring about 15 cm in direction of movement of the patient's bench) to be scanned in about 200 to 250 ms. This enables a complete 3D image to be taken in a single movement phase of the heart, which can result in a significant reduction in the dose compared to earlier methods. However, this “flash mode” only provides a snapshot in a type of “still image” of the heart and therefore does not permit a functional analysis of the heart. For this, as before, it is necessary to produce a whole series of sequential images or EKG-triggered whole images of the heart. However, this results in a correspondingly higher exposure to radiation.